An ordinary photosensitive structure for flexographic printing has a constitution wherein a polyester film is used as a support, and a photosensitive resin is laminated thereon. A method for preparing a plate from a photosensitive structure for flexographic printing adopts steps for exposing an image (relief exposure) on the surface of a photosensitive resin through a transparent image carrier (negative film), washing away unexposed portions using a solvent for the developer, and forming a desired image, i.e., a relief image, to obtain a printing plate. Furthermore, a method wherein the entire surface of a photosensitive resin is exposed to ultraviolet rays through a support (back exposure) to form a thin evenly cured layer, and then relief exposure is performed through a negative film, is also adopted. The thickness of a flexographic plate is usually 0.5 to 10 mm, and the thickness of the plate is suitably selected depending on materials to be printed and the setting of printers.
Although the obtained flexographic plate is used by fixing it on the plate cylinder of a printing machine using a double-sided adhesive tape or the like, a shear stress is produced during printing in the printing plate between the plate cylinder and the impression cylinder. When the printing plate is peeled from the support by the shear stress, a problem in that printing must be stopped or the like is caused. In addition, when the printing plate is removed from the plate cylinder after printing, the photosensitive resin may be peeled off the plate cylinder by pulling, and in such a case, the photosensitive resin and the support are undergone stress. If the support and the photosensitive resin are peeled off, the plate cannot be reused, and another plate must be prepared anew.
From such a point of view, a polyester film, which is a support, and the photosensitive resin must be firmly adhered to each other, and the adhesive strength thereof is preferably 5.9 N/cm or more when the photosensitive resin is forcibly peeled off the support at a peeling angle of 180°. Furthermore, from the viewpoint of the reuse of the plate, it is more preferable that the adhesive strength of 5.9 N/cm or more is maintained even after the photosensitive resin is processed to prepare the plate and is aged.
From such a point of view, methods for forming an adhesive layer between a support and a photosensitive resin layer are proposed in, for example, Patent Document 1 (JP-A-2000-155410) and Patent Document 2 (JP-A-2001-264959). However, in these references, there is limitation in the number of unsaturated bonds of an ethylenically unsaturated compound contained in the photosensitive resin layer, and for the photosensitive resin layer composed of a photosensitive resin composition containing no ethylenically unsaturated compounds described in these references, none of adhesive layers exhibiting a good adhesive strength are described.
In Patent Document 3 (JP-A-4-204447), a photosensitive resin relief-printing material provided with a photo-cured barrier layer to an ink-washing oil on an adhesive-treated support. However, in this case, since an adhesive layer is formed, and a barrier layer is further formed thereon, the step for preparing the photosensitive resin printing material becomes complicated.
As a material for a flexographic plate, Patent Document 4 (JP-A-1-296252) proposes the intervention of an undercoat layer between a support and an adhesive layer. Even in this case, since two layers of the undercoat layer and the adhesive layer are laminated, the step for preparing the flexographic plate material becomes complicated.
In Patent Document 5 (JP-A-2-8849) and Patent Document 6 (JP-A-2-8851), a plate composed of at least one intermediate layer formed on a support and a photosensitive relief layer formed on the intermediate layer is proposed. In these references, although polyvinyl alcohol and polyamide are shown as a binder used as the intermediate layer, a thermoplastic elastomer composed of a monovinyl substituted aromatic hydrocarbon and a conjugated diene is not described.
In Patent Document 6, although an intermediate layer that contains a specific compound is described, the specific compound is monofunctional, and no polyfunctional compounds are described. Further as the effect of the invention, improved adhesiveness and the improvement of developers are described, the resistance to ink solvents required when used as a plate is not described.
In addition, a method relating to the reuse of the rejected plate produced in the production of a flexographic plate is proposed in Patent Document 7 (JP-A-6-214378). In this document, there is described the reuse consisting of a step for isolating a recording layer from a support, a step for pulverizing the recording layer as required, and a step for adding the pulverized material to a synthetic resin mixture. However, the reuse requires a large number of steps, and has become complicated.
As described above, it is the present situation that no photosensitive structures for flexographic printing that has high adhesive strength and excels in production efficiency, and the rejected plate produced in the production process can be easily reused have been found.
Patent Document 1: JP-A-2000-155410
Patent Document 2: JP-A-2001-264959
Patent Document 3: JP-A-4-204447
Patent Document 4: JP-A-1-296252
Patent Document 5: JP-A-2-8849
Patent Document 6: JP-A-2-8851
Patent Document 7: JP-A-6-214378